Cyanobacteria are primitive procaryotic organisms, capable of oxygen-evolving photosynthesis characteristic of plants. Unlike plants, cyanobacteria have a single genetic system involved in photosynthesis as well as all other genetically mediated cellular processes. A major question in plant biology is the origin and composition of the chloroplast genome, which in part directs plant photosynthesis. This proposal addresses this issue by studying the structure and organization of photosynthetic genes in common to plants and cyanobacteria. In previous work, two photosynthetic genes from the cyanobacterium Anabaena were isolated and their nucleotide sequence determined. In the proposed work, this foundation will be built upon by the characterization and cloning of additional photosynthetic genes and a study of their organization. The data so obtained will be compared to currently available sequence data on these genes in plants, to estimate changes in gene structure and organization which have accompanied the evolution of chloroplasts. This research is of fundamental importance to plant biology, agriculture and hence human welfare.